when extruding internal circles not showing

Hi,

I have been sent an outline of a very simple part as a DXF file.

I have imported this into SolidWorks, I have not bothered to fully constrain this part as should be to correct size, with holes in correct position etc

When I go to extrude to its final thickness (60mm) the 30mm dia holes do not show.

It will only extrude the outer shape.

Why would this happen?

SolidworksParts And Features